How-To

Updated December 3, 2007 12:00 PST

Bridge Z-Wave and X10 Protocols

By David Powell

One of the most valuable characteristics of building your
own home automation system is the ability to personalize
it by picking and choosing the devices that meet your needs.
However, there are times when you require a product to perform
a certain function and that product may not exist for the
protocol of your choice.

The history
of the X10 protocol dates back to the mid 1970s and
X10 devices are still in production today. Throughout the
lifetime of X10, engineers and hobbyists have created a
large variety of device types from wall modules to light
switches, motion sensors, water leak detectors, drive way
sensors, and much more. Eventually we will probably see
similar devices available that utilize the Z-Wave protocol,
but until then we can use existing X10 devices to meet our
needs. How can we allow the different protocols to interact
with each other? We do this by bridging the communication
gap between the two protocols using a home automation controller.

The X10 protocol is known as a power line carrier (PLC)
protocol and how
it works is straightforward. In the United States, home-based
power alternates current direction 60 times a second. Each
time it changes direction the voltage at the point of change
is zero. X10 sends data over the home's power lines as close
to this point as possible.

The Z-Wave protocol is known as a wireless mesh network
protocol and it does not rely on the home's power lines
to transmit data. Everything is transmitted using a radio
frequency (RF) signal in the 908MHz signal band.

There is an obvious communications barrier between Z-Wave
and X10. They not only speak different languages but they
also use two very different methods of transportation. So
how do we cross this barrier? By building a bridge using
software or hardware. Basically we need something that speaks
both protocol languages and provides a logic engine.

The inexpensive solution to this problem is to use a software
product such as HomeZix
or HomeSeer.
You would then use a X10 PC controller such as the W800RF
wireless X10 receiver or SmartHome PowerLinc
PLC. Both of these X10 controllers communicate with the
software using the computer's serial port. You would also
need a Z-Wave PC controller, which comes in many varieties
including USB, serial, and Ethernet. HomeZix and HomeSeer
both support speaking the X10 and Z-Wave language and they
both have built-in logic engines.

Let's look at a practical example to try and understand
the needed components. Say we have installed an X10 driveway
sensor and we want that to turn on our Z-Wave light switch
to illuminate our driveway when we come home after dark.
The driveway sensor would send an X10 message to the X10
PC controller, which would then relay the message to your
software. This is where the logic engine comes in to play.
The software allows you to react to events in specific ways
based on the logic you tell it to perform. For example,
you would write a logic statement such as "WHEN driveway
is On AND after-sunset is True THEN turn lights On."
The logic engine allows you to accept input from one type
of device and react by outputting a message to another type
of device. Thus the communication gap has been bridged.

A more expensive, but just as effective, solution to bridging
the communications gap is to use hardware controllers. Hardware
controllers such as the Elk
M1 Gold also contain logic engines that "you,"
the installer, must program. The advantage of using a hardware
controller is they are typically more reliable and consume
less power than leaving a PC on. There are hardware solutions
in development that will likely be less expensive than those
I've already mentioned. One of these is the Wayne-Dalton
X-10 Bridge Controller, which, according to the company,
is coming soon.

This introduction was created to lay the foundation for
subsequent tutorials. In my next article I will walk you
through the details of creating a bridge between X10 and
Z-Wave using the Elk M1G and related components. I've created
a bridge in my own home automation system utilizing a W800RF
X10 receiver and an EagleEye X10 motion sensor. I placed
the motion sensor underneath the dashboard of my car as
an extra layer of security. When the motion sensor is turned
on the Elk M1 security system makes an announcement and
turns on the Z-Wave enabled lighting in my home. I'll describe
this setup in more detail in my next article. Stay tuned.